Play Framework / Scala：抽象存儲庫和Json de / serialization

Question

這個問題可能與Scala有關，而不僅僅是Play，但問題在於：我正在嘗試為常見的DB操作實現存儲庫的抽象。

trait Entity {
  def id: UUID
}

trait Repository[T <: Entity] {

  val JSON_KEY_ID = "_id"

  def collection: JSONCollection

  def insert(t: T): Future[Either[String, T]] = {
    collection.insert(t).map(wr => if (wr.ok) Right(t) else Left(wr.getMessage()))
      .recover { case t => Left(t.getMessage) }
  }

   def update(t: T): Future[Either[String, T]] = {
    val selector = Json.obj(JSON_KEY_ID -> t.id.toString)
    collection.update(selector, t).map(wr => if (wr.ok) Right(t) else Left(wr.getMessage()))
      .recover { case t => Left(t.getMessage) }
  }
}

然后，我有想要與之配合使用的對象：

case class UserDAO(id: UUID) extends Entity[UserDAO]

object UserDAO {
  val JSON_KEY_ID = "_id"

  implicit val userDaoWrites: OWrites[UserDAO] = new OWrites[UserDAO] {
    def writes(user: UserDAO): JsObject = Json.obj(
      JSON_KEY_ID -> JsString(user.id.toString)
    )
  }

  implicit val userDaoReads: Reads[UserDAO] = (
    (__ \ JSON_KEY_ID).read[UUID]
    )(UserDAO.apply _)
}

然后像這樣定義它的存儲庫：

class UserRepository @Inject()(val reactiveMongoApi: ReactiveMongoApi) extends Repository[UserDAO] {
  val db = reactiveMongoApi.db
  override def collection: JSONCollection = db.collection[JSONCollection]("users")
}

我得到的錯誤是

No Json serializer as JsObject found for type T. Try to implement an implicit OWrites or OFormat for this type.
collection.insert(t).map(wr => if (wr.ok) Right(t) else Left(wr.getMessage()))
                 ^

我試圖提供implicit OWrites[T] ，甚至提供implicit OWrites[T] implicit OWrites[_]無濟於事。 也許我想要實現的目標是不可能的。 如果沒有，我該如何解決？ 非常感謝你。

Answer 1

您應該能夠只使用上下文綁定。

trait Entity {
  def id: UUID
}

class Repository[T <: Entity : Writes] {
  ...
}

這將確保如果作用域中存在隱式的Writes[T] ，它將可用於您的插入和更新功能。